A known direct smelting process for a metalliferous material, which relies principally on a molten bath as a smelting medium, and is generally referred to as the HIsmelt process, is described in International application PCT/AU96/00197 (WO 96/31627) in the name of the applicant.
The HIsmelt process as described in the International application in the context of direct smelting a metalliferous material in the form of iron oxides and producing molten iron includes the steps of:
(a) forming a bath of molten iron and slag in a direct smelting vessel;
(b) injecting into the bath: (i) metalliferous material, typically iron oxides; and (ii) solid carbonaceous material, typically coal, which acts as a reductant of the iron oxides and a source of energy; and
(c) smelting metalliferous material to iron in the molten bath.
The term “smelting” is herein understood to mean thermal processing wherein chemical reactions that reduce metal oxides take place to produce molten metal.
The HIsmelt process also includes post-combusting reaction gases, such as CO and H2 released from the bath, in the space above the bath with oxygen-containing gas, typically air, and transferring the heat generated by the post-combustion to the bath to contribute to the thermal energy required to smelt the metalliferous materials.
The HIsmelt process also includes forming a transition zone above the nominal quiescent surface of the bath in which there is a favourable mass of ascending and thereafter descending droplets or splashes or streams of molten metal and/or slag which provide an effective medium to transfer to the bath the thermal energy generated by post-combusting reaction gases above the bath.
In the HIsmelt process metalliferous material and solid carbonaceous material are injected into a molten bath through a number of solids injection lances (sometimes referred to as “tuyeres”) which are inclined to the vertical so as to extend downwardly and inwardly through a side wall of a direct smelting vessel and into a lower region of the vessel so as to deliver at least part of the solids material into a molten metal layer in the bottom of the vessel. To promote the post-combustion of reaction gases in an upper part of the vessel, a blast of hot air, which may be oxygen-enriched, is injected into an upper region of the vessel through a downwardly extending hot air injection lance. Off gases resulting from post-combustion of reaction gases in the vessel are taken away from the upper region of the vessel through an off gas duct. The vessel includes refractory-lined water cooled panels in the side wall and the roof of the vessel, and water is circulated continuously through the panels in a continuous circuit.
The HIsmelt process enables large quantities of molten iron to be produced by direct smelting of metalliferous material in a molten bath. To enable such levels of production, large quantities of both metalliferous material and carbonaceous material must be supplied to the vessel.
The above description is not to be taken as an admission of the common general knowledge in Australia or elsewhere.
U.S. Pat. No. 6,989,042 in the name of the applicant discloses parameters for injecting feed materials (solid material and carrier gas) into a molten bath via solids injecting lances in the HIsmelt process. These parameters include injection velocity, lance diameter, lance orientation, and superficial gas flow from the metal layer as a consequence of the solids injection.
Specifically, claim 1 of the US patent defines the steps of a direct smelting process for producing metals which term includes metal alloys from a ferrous material which includes the steps of:                (a) forming a bath of molten metal and molten slag in a metallurgical vessel;        (b) injecting feed materials being solid material and carrier gas into the molten bath at a velocity of at least 40 m/s through a downwardly extending solids injection lance having a delivery tube of internal diameter of 40-200 mm that is located so that a central axis of an outlet end of the lance is at an angle of 20 to 90 degrees to a horizontal axis and generating a superficial gas flow of at least 0.04 Nm3/s/m2 within the molten bath (where m2 relates to the area of a horizontal cross-section through the molten bath) at least in part by reactions of injected material in the bath which causes molten metal to be projected upwards as splashes, droplets and streams and form an expanded molten bath zone, the gas flow and the upwardly projected molten material causing substantial movement of material within the molten bath and strong mixing of the molten bath, the feed materials being selected so that, in an overall sense, the reactions of the feed materials in the molten bath are endothermic; and        (c) injecting an oxygen-containing gas into an upper region of the vessel via at least one oxygen gas injection lance and post-combusting combustible gases released from the molten bath, whereby ascending and thereafter descending molten material in the expanded molten bath zone facilitate heat transfer to the molten bath.        
The applicant has determined that achieving the required extent of upward flow of molten material from the metal layer is a difficult issue as the size of direct smelting vessels increases. In particular, in a vessel with an equivalent hearth diameter of 6 m or more, the mixing requirement is significantly more difficult to achieve than is the case with a smaller vessel at roughly half this equivalent diameter. Moreover, the applicant has determined that achieving the required extent of upward flow of molten material from the metal layer is critical to stable and cost effective operation of the HIsmelt process at the larger scale.
The applicant has realised that the required extent of upward flow of molten material can be achieved by selecting the operating parameters for the HIsmelt process so that feed material (solid material and carrier gas) for the process have sufficient momentum to penetrate to a depth of at least 100 mm into a metal layer of a molten bath that is at least 900 mm deep.
Numerical calculation to achieve a given penetration depth into the metal layer is not an exact science. Different penetration depths can be calculated (for nominally the same conditions) using different calculation assumptions and methods. For the purpose of clarifying the meaning of the term “penetration depth”, a standard calculation method based on a model from McMaster University in Canada has been adopted. Details of this model are given in the appendix, and the model itself is freely available. The term “penetration depth” as used here is implicitly defined as the depth of penetration calculated using the McMaster model as described in the appendix. Hence, the reference to penetrating at least 100 mm into the metal layer of the molten bath in the preceding paragraph means a penetration depth of at least 100 mm as calculated using the McMaster model as described in the appendix.
The present invention provides a molten bath-based process for direct smelting metalliferous material and producing molten metal in a direct smelting vessel that contains a molten bath that has a metal layer that is at least 900 mm deep includes selecting operating parameters of the process so that feed material including solid material and carrier gas is injected from above the metal layer into the metal layer via at least one solids injection lance with sufficient momentum to penetrate to a depth of at least 100 mm below a nominal quiescent surface of the metal layer to cause upward movement of molten material and gas from the metal layer.
The operating parameters for the process to provide feed material with sufficient momentum may include injecting feed material with a lance pressure drop of at least 1 bar in the solids injection lance or lances.
The lance pressure drop in the solids injection lance or lances is a measure of the acceleration and therefore the momentum and/or velocity of feed material through the solids injection lance or each solids injection lance.
The term “lance pressure drop” is understood herein to mean the pressure drop from a point (A) upstream of the lance and the “acceleration section” of the lance (see below) where gas velocity is at least a factor of 2 lower than that at the outlet lance tip to (B) the outlet lance tip itself. In many cases pressure at point (B) is not available (e.g. no pressure sensor at this location), but in such cases lance tip pressure can be reasonably calculated from pressure above the melt via estimated slag density and lance tip immersion depth.
The term “acceleration section” is understood herein to mean a section of a lance in which the superficial gas velocity of feed material passing through the section changes by a factor of at least two from an inlet end to an outlet end of the section.
The lance pressure drop may be at least 1.5 bar in the solids injection lance or lances.
The lance pressure drop may be at least 2 bar in the solids injection lance or lances.
The lance pressure drop may be at least 3 bar in the solids injection lance or lances.
The operating parameters for the process to provide feed material with sufficient momentum may include positioning a lower end of the solids injection lance or each solids injection lance as close as possible to a metal/slag interface.
The operating parameters for the process to provide feed material with sufficient momentum may include selecting the operating parameters of the process, such as the slag chemistry, to promote the formation of pipe extensions of the solids injection lance or lances to thereby minimise the travel distance of injected solid material through the lance or lances and thereby facilitate positioning the lower end of the or each solids injection lance as close as possible to the metal/slag interface.
The operating parameters for the process to provide feed material with sufficient momentum may include an injection velocity of at least 40 m/s for injected feed material.
The operating parameters for the process to provide feed material with sufficient momentum may include an injection velocity of at least 50 m/s.
The operating parameters for the process to provide feed material with sufficient momentum may include an injection velocity of at least 60 m/s.
The operating parameters for the process to provide feed material with sufficient momentum may include a solids/gas ratio of injected solid feed material and carrier gas of at least 10 kg solids per Nm3 gas.
The operating parameters for the process to provide feed material with sufficient momentum may include a solids/gas ratio of injected solid feed material and carrier gas of at least 15 kg solids per Nm3 gas.
The solids injection lance or lances may have an internal diameter of at least 40 mm.
The solids injection lance or lances may have an internal diameter of at least 60 mm.
The solids injection lance or lances may have an internal diameter of at least 80 mm.
The solids injection lance or lances may have an internal diameter of more than 200 mm.
The solid feed material may be a solid carbonaceous material only. The solid carbonaceous material may be coal.
The solid feed material may be a solid carbonaceous material and a flux only.
The solid feed material may be a metalliferous feed material and a solid carbonaceous material.
The solid feed material may be a metalliferous feed material, a solid carbonaceous material, and a flux.
The metalliferous feed material may be an iron-containing material.
The iron-containing material may be iron ore.
The iron ore may be in the form of fines.
The metalliferous feed material and the solid carbonaceous material may be injected through the same solids injection lance or lances or through separate solids injection lances.
The metalliferous feed material may be pre-heated.
The metalliferous feed material may be at ambient temperature.
The carrier gas may be an inert gas, such as nitrogen or argon.
The penetration depth of feed material into the metal layer may at least 150 mm.
The penetration depth into the metal layer may at least 200 mm.
The penetration depth into the metal layer may at least 300 mm.
The penetration depth into the metal layer may be less than 500 mm.
The penetration depth into the metal layer may be less than 400 mm.
The metal layer depth may be at least 1 m.
The metal layer depth may be at least 1.5 m.
The metal layer depth may be less than 2.5 m.
The solids injection lance or lances may be arranged to extend downwardly into the vessel with a central axis of an outlet end of the lance or lances at an angle of 20-90 degrees to a horizontal axis.
The solids injection lances may include an opposed pair of solids injection lances that are oriented within the vessel and are arranged so that injection of feed materials via the lances forms overlapping plumes of injected feed material in the metal layer of molten bath.
The solids injection lances may include at least one pair of opposed injection lances extending downwardly and inwardly into the molten bath with longitudinal axes of the lances intersecting at a floor of the vessel or above the floor or below the floor so that plumes of injected material from the lances overlap in a central region of the metal layer that is at least 100 mm the surface of the metal layer and there is upward movement of molten material and gas from the central region of the metal layer.
The term “plumes of injected material” is understood herein to describe the streams of (a) injected feed material and (b) products produced as a result of such injection into the direct smelting vessel via the lances. In situations where the feed material includes solid carbonaceous material, the products include, by way of example, volatiles released from the carbonaceous material and reaction products such as CO and CO2 and H2O.
The vessel may have a diameter of at least 6 m.
The vessel may have a diameter of at least 7 m.